[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
----- Original Message -----
From: "Sim Koning" <email@example.com>
To: "jrc" <firstname.lastname@example.org>; <email@example.com>
Sent: Thursday, September 25, 2008 7:34 PM
Before I continue, does anyone know if a 5 ounce Archaeopteryx could carry a
1 pound coconut?
..........Probably depends largely on how well the backpack is constructed
Orstriches have large wings (relatively speaking), but they have completely
lost their flight feathers, which have been replaced with soft downy
insulatory feathers that they also use for display.
Date: Thu, 25 Sep 2008 04:30:00 -0600
----- Original Message -----
From: "Sim Koning"
Sent: Wednesday, September 24, 2008 11:54 PM
Even so, ostriches use their wings to assist in turning while running.
Drag by definition is resistance to an object moving through fluid, which
must be overcome by thrust which in turn (in the case of a wing) produces
lift: so basically it would slow them down if they extended their wings.
If they leapt into the air, these "wings" would actually slow them down
due to drag,
........... As I said before, feathers can be used to modify form drag. For
example, modifying an essentially circular cross-sectional shape into a
shape that more closely resembles an airfoil (in cross section, not
planform) can reduce drag by a factor of as much as 25. Therefore,
extending arms WITHOUT feathers can have a drag penalty as much as 25 times
greater than exending the same arm if it does have feathers.
This would explain why many flightless birds have completely lost their
flight feathers and have extremely reduced wings.
............I tend to suspect that the driving force behind those changes is
the reduced biological cost of the moult.
Why presume that the early wings make them less streamlined when jumping?
Would you race a motorcycle while wearing a cape?
...........Why use a non-applicable analogy?
I imagine it would have a similar effect If the earliest forms had simple
elongated protofeathers, or even primitive flight feathers for that matter.
Yes a simple wing could extend their jump, but it would also slow them down
due to drag
...........Actually, once clear of the ground it can be used to speed them
up even when gliding, by their conversion of potential energy back to
kinetic, and by the reduction in form drag when the arms are extended.
Yes, which is possibly why the wings could be oriented to modulate or
increase traction rather than reduce it.
Why haven't flightless birds kept this feature? The only birds that do this,
do it to run up trees and then jump out of them.
.........Ostriches do it.
If they leapt into the air, they would rapidly decelerate, making them
........Once in the air, the wings can be positioned to allow the animal to
accelerate on its way back to the ground. Note that I'm not saying that
they would use the double-diamond configuration that allows speeds over 240
mph, but they can be used to allow horizontal speeds well over that which
can be achieved by running (high wingloading helps in that regard).
Since many improvements in parachuting and/or gliding ability don't lead
toward the direction of powered flight, doesn't that create problems for
How do you know this? If a gliding rodent begain evolving extended webbed
fingers it could gradually lead to the same condition seen in bats.
Sometimes the only difference between a gliding aircraft and an airplane is
one has thrust, one does not; otherwise the wing design is largely the same.
In fact some gliders have engines that are used occasionally. A highly
efficient gliding animal could probably reach a state of sustained flight by
simply using the wind; from that point it would only need to develope way of
............. Well, no machine or animal can extract extended flight energy
from a uniform wind when no shears are present, and it takes a pretty
derived wing/control system to extract energy from the chaotic processes
that result in microlift (as just one example of atmospheric processes that
can be used to enable flight). My point was that improvements in
proto-gliding capability lead toward glding adaptations that make the
powering of flapping flight more difficult. I note in passing that large
soaring birds didn't develop until after the pterosaurs were gone, so
apparently at least some early birds were better flappers than soarers.
How many apes seem to be developing sapience?
........ Most ?
Which jump out of water to escape predatory fish. What are these protobirds
doing, jumping up to a convenient biting hight for a 10 foot tall theropod?
...........Once in the air, they would rapidly accelerate away from the big
guy's reach (that high wingloading again). Even a one percent increase in
escape rate would pay off over the long haul.
If they are jumping to catch prey, the immediate drop in velocity due to
drag would cancel out any benefit for a cursorial predator.
..........Why not just jump higher than the prey and use the rapid
acceleration due to high wing loading to overtake him in the air? Peregrine
falcons have taken this to the point of passing their prey in the air,
turning around upside down with extended claws, and slowing so that the prey
runs right into their grasp. I can't see an early bird taking it to that
extent, but it's a fascinating example of an extreme.
Which demonstrates that there is more than one way to skin a cat. A good
place to mention that the ground up vs. trees down scenario is a perfect
example of a potentially false dichotomy.
..........Have I said that before? It bears repeating. Any animal that is
developing flight can access more varied sources of energy as the ability
develops, whether that energy be potential, kinetic, or chemical.
- From: Sim Koning <firstname.lastname@example.org>